New Zealand dual star Sonny Bill Williams denies he's made a decision remain in rugby league for one more season.

There were rumours the 27-year-old would return to rugby union - with the Chiefs his most likely destination - but according to reports from Australia, Williams has agreed to sign another one-year contract with the Sydney Roosters, believed to be worth about $1 million.

Williams, who played 19 tests for the All Blacks, has been in fine form since he returned to rugby league this year and was the standout performer in the Roosters' 18-12 victory over the Manly Sea Eagles on Monday night.

While it's reported the finer details of the contract have yet to be ironed out, the Sydney-based Daily Telegraph says influential Roosters chairman Nick Politis is playing a major role in convincing Williams to stick with his side.

The reported contract is also believed to be flexible when it comes to Williams' other sporting interests, mainly boxing.

However, the player himself denies any deal has been done. Taking to Twitter late this morning, Williams said nothing had been signed and his sole focus was the current NRL season.

"I have not signed or committed to anything for next year and I won't be doing so until I feel the time is right," he tweeted.

"My sole focus right now is playing the best I can for the boys and the club.."

Earlier this week Roosters coach Trent Robinson implored Williams to stay in rugby league, hoping he would not be lost to the code like fellow dual star Israel Folau.

"Sonny's added huge value to the Roosters and also to our game," Robinson said.

"Even I'm switching over and watching Israel Folau play. We're all enjoying watching him play - there's a sense of pride when he plays well for every rugby league supporter.

"We don't want that to happen Sonny ... going to watch him play with another code.

"We want to keep them in our game - we need to keep them in our game."

Asked about the importance of keeping Williams in the NRL, chief executive Dave Smith said: "We want people in our game like Sonny Bill and of course we want him to stay.

"He's one of many wonderful athletes in our game, you got 'GI' (Greg Inglis), Sonny Bill . . . the list is endless."